The present invention relates generally to cellulosic fibers and, more specifically, to crosslinked cellulosic fibers having high wet bulk.
Cellulosic fibers are a basic component of absorbent products such as diapers. Although absorbent, cellulosic fibers tend to retain absorbed liquid and consequently suffer from diminished liquid acquisition rate. The inability of wetted cellulosic fibers in absorbent products to further acquire liquid and to distribute liquid to sites remote from liquid insult can be attributed to the loss of fiber bulk associated with liquid absorption. Bulk is a property of fibrous composites and relates to the composite""s reticulated structure. A composite""s ability to wick and distribute liquid will generally depend on the composite""s bulk. The ability of a composite to further acquire liquid on subsequent insults will depend on the composite""s wet bulk. Absorbent products made from cellulosic fluff pulp, a form of cellulosic fibers. having an extremely high void volume, lose bulk on liquid acquisition and the ability to further wick and acquire liquid, causing local saturation.
Crosslinked cellulosic fibers generally have enhanced wet bulk compared to noncrosslinked fibers. The enhanced bulk is a consequence of the stiffness, twist, and curl imparted to the fiber as a result of crosslinking. Accordingly, crosslinked fibers are advantageously incorporated into absorbent products to enhance their bulk and liquid acquisition rate and to also reduce rewet.
Because absorbent products ideally rapidly acquire liquid, effectively distribute liquid to sites remote from insult, continue to acquire liquid on subsequent insult, and have low rewet, there exists a need for cellulosic fibers having wet bulk sufficient to achieve these ideal properties. The present invention seeks to fulfill these needs and provides further related advantages.
In one aspect, the present invention provides individualized cellulosic fibers having high wet bulk. The high wet bulk cellulosic fibers of the invention are glyoxal crosslinked cellulosic fibers. In one embodiment, cellulosic fibers are preferably catalytically crosslinked with a combination of glyoxal and propylene glycol. In another embodiment, the fibers are crosslinked with a combination of glyoxal and a glyoxal-derived resin selected from a glyoxal/polyol condensate, a cyclic urea/glyoxal/polyol condensate, and a cyclic urea/glyoxal condensate.
In another aspect of the invention, methods for the preparation of cellulosic fibers having high wet bulk are provided. In the methods, a fibrous web of cellulosic fibers is treated with a glyoxal crosslinking combination, wet fiberized, and then dried and cured to provide individualized cellulosic fibers having high wet bulk. Generally, fibers prepared by the method of the invention have a wet bulk that is greater than about 20 cc/g at 0.6 kPa, or at least about 30 percent, and preferably at least about 50 percent, greater than commercially available high-bulk fibers.